Thank you Cathal! I must say, we're wandering in the dark here. I don't know how to add that module to a page, as its install instructions say. Does this mean the UI it offers, for configuring the URL rewriter, needs adding to an Admin page as a module, rather like a block of content is added to a user facing page? (I haven't done that either, we've been delivered a DNN site by a third party and are learning as we go). We'll try this soon.
We have actually gone to extremes, and set up three independent sites within our IIS installation. We created a single IIS site on port 80 with nothing but a few rewrite rules, which forward some requests to our coreproduct site, and the rest to a DNN site. This has introduced a long series of drawbacks, because the DNN site frequently writes its HTTPAlias or PortalAlias into HTML it outputs, which is dnn.localhost in our case, so the rewriting site has to have some (probably horribly inefficient) outbound rewrite rules to alter dnn.localhost to our main domain name, so the HTML served to the browser contains the proper names.
This is a particular pain with editing pages, where the POST when saving an edit makes a POST to e.g.
and responds with something like:
Our solution to this is to make the internal domain name the same number of characters as the public domain name, i.e. something like 'foobar.arse' instead of 'oursite.com', and use an outbound rewrite rule to rewrite the response, leaving the magic number alone because it still represents the right number of characters.
All in all this rewrite module and its apparant lack of configuration documentation has been a huge pain.